The X-Men #28

Banshee's premier issue starts off with him as an apparent villain, teamed up with Ogre who is working for Factor Three. However while Ogre is working on a way to track the X-men, Banshee goes into town, stealing a priceless painting called Gaelic Landscape.The X-men are testing Mimics powers after Professor X enhanced the range in which Mimic must be in order to "mimic" a mutants power. After the tests are finished, Professor X uses Cerebro to look for mutant activity. He discovers Banshee stealing imported tobacco.Ogre, with the help of Banshee launches a unsuccessful kidnap attempt on the Professor X. After a silver-age style epic battle, the X-men capture Banshee and defeat Ogre. It is then revealed that Banshee was controlled by Ogre through one of his many gadgets.This issue ends on the note that Factor Three is still out there....This story is reprinted in Essential Classic X-Men Vol. 2